The study area
Cyprus (35°00′N, 33°00′E), is the third largest island in the Mediterranean Sea covering an area of 9250 km2 (Fig. 1). The location of the island, with Africa to the south, Turkey and central Europe to the north and the Middle East to the east, is very important for the avifauna of the island. Cyprus includes a diversity of habitats such as sand dunes and rocky coastline, wetlands, streams and lakes, scrubland, agricultural land (e.g. cereal fields, orchards, vineyards), desert-like uncultivated or rocky land, and forests (mostly pine forests) [26].
The locations sampled are presented below. The respective names are indicated in Fig. 1.
Group 1. Mountain with Pinus brutia pine forests and maquis
Apliki
A nest was found in a Quercus alnifolia zone, with pines and maquis (1000 m asl).
Potamitissa
A natural nest was found in a cavity of an oriental plane tree in a clump of trees (alders, plane, pine and olive trees) and scattered low vegetation of thorny shrubs (820 m asl).
Athrakos
An artificial nest placed on a pine tree was in use and pellets were collected from a nearby roost. Sparse vegetation with Cistus shrubs and some arable land surrounded the sites (676 m asl).
Prastio Kellakiou
An artificial nest was in use placed in a hilly area covered with a variety of natural vegetation, such as Quercus alnifolia, Cistus sp., Eucalyptus sp., fruit and pine trees, and cypress trees (490 m asl).
Pelentri
An artificial nest was in use situated on a pine tree in an area of scarce pine trees, Quercus alnifolia, Cistus sp. and fruit trees (800 m asl).
Lefkara
An artificial nest was in use situated under a bridge in an area surrounded with pine trees, cypresses trees and reedbeds (430 asl).
Group 2. Lowlands with agricultural crops
Avdimou
An artificial nest on a pine tree in a lowland area was in use. Reedbeds surrounded the area (380 m asl). Another artificial nest placed in the same area on an electric power pole was also in use.
Paramali
An artificial nest in use was situated on a cypress tree on cultivated land (20 m asl).
Agios Dimitrianos (Episkopi)
Two nests were located on pine trees surrounded by cultivations, scattered pines and fruit trees (23 m asl).
Pareklisia
A roost site was found in a rocky area near habitations, sparse vegetation and cultivations with Pistacia lenticus.
Avdellero
A nest was placed under a bridge within a livestock grazing area (135 m asl).
Achelia
Four artificial nests placed on cultivated land were in use (35 asl).
Timi
An artificial nest in use was situated in a forest surrounded by cultivations and low vegetation at about sea level.
Makounta
A nest was found in a craggy mountainous area. The surrounding habitat was dominated by agricultural and tree cultivations (100 m asl).
Group 3. Hilly areas with crops and livestock facilities
Kofinou
An artificial nest in use was placed near livestock areas. The surrounding vegetation was composed of cultivated trees (mainly almond) and low shrubs (169 m asl).
Anglisides
An artificial nest and roost sites in use were under a stone-built bridge. Reedbeds, acacias and olive trees were the most important vegetation around this site (174 m asl).
Klavdia
An artificial nest was in use was placed under a bridge. The surrounding habitat was similar to Anglisides (170 m asl).
Kellia
An artificial nest in use was placed under a bridge in an area with riparian vegetation of reedbeds and acacias (55 m asl).
Panagia Aimatousa
A roost site was located near livestock facilities in an area surrounded by olive trees.
Group 4. Areas with dry vegetation
One roost site was found near Zodia (85 asl) and three at Pano Koutrafas (241 m asl), in dry craggy areas with bushes, acacias and some fruit tree cultivations.
Group 5. Mountainous areas with vineyards and olive trees
Trachypedoula
A roost was found on a stone-built bridge. The surrounding area included vineyards, olive cultivations and bushland (500 m asl).
Vretsia
Two nests were located in deserted buildings in a village. Nearby areas were covered with vineyards and citrus fruit cultivations (500 m asl).
Group 6. Lowlands with maquis vegetation
Kouklia
Roosts were located on a bridge and nearby areas surrounded with maquis and olive and carob trees.
Pellet collection
Available evidence indicates that pellet analysis is still the most suitable method for studying the diet of owls especially the medium sized ones [9, 27, 28]. Analysing a small sample of pellets can give adequate information about prey composition in the field and it takes less working hours than mammal trapping [29, 30]. Despite the controversy whether pellets represent the true community structure of the prey [15], pellets can give information about prey-species communities and other biogeographic data [1, 31, 32]. Pellets are relatively easy to find and small bones remain well preserved within them [2]. Pellet analysis is a useful tool for the management and protection of owl species and their habitats [1] while the outcome from the analysis can be used to assess ecosystem health [2, 33].
Pellets were collected at the end of every season for 1 year, from summer 2013 to summer 2014. They were collected from natural nests (situated at old buildings, tree cavities and under bridges) and nesting boxes placed and monitored by the Game and Fauna Service. The nests were located at a variety of habitats, including coastal areas, lowlands (0–500 m elevation) and mountain areas (above 500 m elevation) with different types of vegetation (see above for a detailed presentation of the localities).
Data analysis
The pellets were analyzed using reference books [34,35,36], but excluding those that contained only hair. Mean weight of each prey taxon was taken from the literature [37, 38]. Mice of the genus Mus and rats Rattus were not identified at the species level because it was impossible to distinguish them by cranial characters. Although their identification could be possible through DNA analysis of hair found in the pellets, this approach was beyond the scope of the present study. Rats most likely belonged to the species Rattus rattus as the presence of Rattus norvegicus on Cyprus is dubious [36]. Insects were identified at the level of family due to the poor condition of their remains in the pellets. The diet of the barn owl was described in terms of seasonal average biomass and numerical percentages of each prey species. Average prey weight of each species in each period was estimated by multiplying the numbers of each prey item by its mean weight, adding the weights produced and dividing the sum by the total numbers of prey in each sample. The diet of barn owl was analysed for each field sample in terms of numbers and biomass. Median prey weights were compared among different seasons by Kruskal–Wallis test. These tests were performed using R [39] and Statistica version 7.0 (StatSoft, Tulsa, USA) softwares. The prey diversity was estimated at a class level (mammals, birds, insects) by using the antilog of the Shannon-Weiner index [40, 41], while the evenness index for the mammals was calculated by using the Hill’s ratio [42, 43].
The prey types were assigned to six major habitat types with regard to elevation, vegetation and human uses (Fig. 1). Principal component analysis was performed on the prey biomass proportions data from the six habitat types. The analysis showed that 99.6% of the variation in the dataset was explained by the first three components while the first two components explain 77.9% of the variance in the data. Only the first 2 components were considered in the analysis based on the Kaiser stopping rule, i.e. the number of components with eigenvalues over 1 [44].